Fortress in K+B vs Q Endgame

''A bishop and a knight usually lose, but some very rare exceptions exist; one of them should be remembered.'' says IM Dvoretsky in his famous Endgame Manual.

The positions of Black's king and queen are irrelevant. The combination of bishop on b2 and a knight on d4 covers the squares a3, b3, c3, c2 and c1, creating an impassable barrier for Black's king. Also it's not possible to force to White into zugzwang. (Also please notice how White's pieces protecting each other.)

Now let's check Karstedt's position. ( The chess composer who discovered this possibility)

A fascinating concept but it's nearly impossible to happen in an actual chess game right? I would agree with you a few days ago but it happened one of my games lately. In fact this is why I'm making this post.